This invention relates to an improvement of a laser beam machine for machining a metal workpiece with a laser beam.
FIG. 12A is a perspective view showing a conventional laser beam machine with five axes X, Y, Z, C and A, and FIG. 12B is also a perspective view showing the machining head of the apparatus. In FIG. 12, a reference numeral 1 designates a laser oscillator for generating a laser beam; 2, a laser beam machine body; 3, a machining head having a focusing lens and a machining gas nozzle; 4, a machining table; and 5, a control unit for controlling the laser oscillator and the machine body. As shown in FIG. 12B, the machining head 3 has a Z-axis moving vertically, C-axis and Z-axis, thus being able to take any posture.
FIG. 13 is a block diagram showing the arrangement of the above-described control unit 5. In FIG. 13, reference character 5a designates a memory in which machining programs have been stored; 5b, a reading device provided for the memory 5a; 5c, a buffer; 5d, a function of analyzing an instruction set in the buffer; 5e, a function of generating a move instruction according to the result of analysis by the function 5d; 5f, a motor control function of transmitting the move instruction to a drive motor; 5g, a drive amplifier; 5h, the motor; and 5i, a position detector for detecting the number of revolutions of the motor.
The operation of the conventional laser beam machine thus constructed will be described with reference to FIG. 14A. The laser oscillator 1 outputs a laser beam 6. The laser beam 6 thus outputted is reflected by a reflecting mirror 7 in the optical path, and concentrated into an optical spot at the focal point by the focusing lens 8 in the machining head 3, thus providing high energy required for machining a workpiece 9 set on a machining table 10. The laser beam thus concentrated is applied vertically to the workpiece 9 on the machining table 10, so that the temperature of the workpiece reaches the melting point where irradiated by the laser beam; that is, the workpiece is molten along the machining locus. The molten material is removed from the workpiece by jetting a machining gas to it. In FIG. 14A, reference numeral 11, an NC (numerical control) device for moving the machining table 10 in an X-Y plane. In FIG. 14B, reference numeral 12 designates an 0-ring; 13, a lens retainer; 14, a machining nozzle; 15, an assist gas inlet; and 16, an assist gas.
The control unit 5 operates according to a machining program corresponding to a configuration to be machined, which is stored in the memory 5a, to drive the motor 5h, thereby to machine the workpiece as required.
When the workpiece is machined as described above, then drag lines 17 are formed in the machined surface of the workpiece 10 as shown in FIG. 15A. This will be described in more detail. The workpiece reacting with the assist gas 16 is molten by the high energy of the laser beam concentrated into the light spot reacting with the assist gas 16. The resultant molten material is caused to flow down the workpiece by the jet stream of assist gas, thus leaving as sparks 18 from the lower surface of the workpiece 9. That is, the drag lines 17 are the traces of the molten material which are formed in the cut surface of the workpiece when flowing down as was described above. The laser beam 6 is applied perpendicularly to the workpiece 9; however, it is moved in a workpiece machining direction 20. This is why the drag lines 17 are curved backwardly, or in the direction opposite to the workpiece machining direction.
The conventional laser beam machine is constructed and operated as described above. The direction of application of the laser beam is perpendicular to the surface of the workpiece 9 at all times. Therefore, the drag lines 17 are curved in the opposite direction to the machining direction with the increasing machining speed, and the sparks 18 formed are also caused to flow a relatively long distance backwardly along the lower surface of the workpiece 9. As a result, the sparks 18, i.e., the molten material will not come off the lower surface of the workpiece 9; that is, a large quantity of burr-shaped dross is stuck to the lower surface of the workpiece 9. This will make it difficult to machine the workpiece satisfactorily, and will make it impossible to further increase the machining speed.
FIG. 16 is a graphical representation indicating the relation between the machining speed V and the degree of curve L of the drag line in machining a workpiece of SPSS 1 mm in thickness with a focusing lens having focal length of 9.525 cm and a 1 kW laser beam applied perpendicularly to the workpiece. As is apparent from FIG. 16, as the machining speed V increases, the degree of curve L of the drag line is increased. At a machining speed of 14 m/min, the degree of curve L is as large as 0.8 mm. In this case, the sparks 18 appearing on the lower surface of the workpiece will flow a relatively long distance in the opposite direction to the machining direction 20 being substantially in parallel with the lower surface of the workpiece. As a result, the molten material appearing as the sparks 18 is fixedly stuck to the lower surface of the workpiece. Thus, under the above-described conditions, the machining speed is limited to 14 m/min. As is apparent from the above description, in the conventional technique in which the incident angle of the laser beam to the workpiece is 90.degree. , the increase of the machining speed V is limited to some extent with the laser output increased.
In the above-described conventional laser beam machine, the positional relationship between the machining head and the workpiece 9 is maintained unchanged during machining. Therefore, in the case of cutting a configuration including curves, it will take a lot of time to form the machining program. Accordingly, a configuration to be cut is limited to a straight line or a simple one consisting of straight lines. This is another difficulty accompanying the conventional laser beam machine.
SUMMARY OF THE INVENTION
Accordingly, an object of this invention is to eliminate the above-described difficulties accompanying a conventional laser beam machine.
More specifically, an object of the invention is to provide a laser beam machine in which the quantity of dross is decreased which may be stuck to the workpiece when the machining speed is increased; that is, the machining speed can be increased, and with a given machining program read, the laser beam is applied to the workpiece at a predetermined angle with the machining direction at all times.
The foregoing object and other objects of the invention have been achieved by the provision of a laser beam machine comprising a laser oscillator for generating a laser beam, a machining head for concentrating the laser beam and applying the laser beam thus concentrated to a workpiece, a machining table on which a workpiece is mounted, and a control unit for controlling the movement of the machining table in an X-Y plane;
in which, according to one aspect of the invention, the machining head has a plurality of reflecting mirror and a focusing lens, which is movable in parallel with a machining direction in a plane perpendicular to the optical axis of the laser beam so that the laser beam applied to the workpiece by the machining head is inclined with respect to the workpiece in the machining direction; and
in which, according to another aspect of the invention, the control unit has a memory for storing data such as the angles of inclination of the laser beam and an inclination correcting function of correcting the amount of inclination of the laser beam according to the machining direction and the posture of the machining head so that, when being moved according to a machining configuration, the laser beam is kept inclined in the machining direction at all times, and the control unit further comprises an inclination calculating function and a physical constant table memory to read the material and thickness of the workpiece and a machining speed from the machining program thereby to determine the most suitable angle of inclination.
A technique of inclining a laser beam with respect to a workpiece has been disclosed by Japanese Patent Application (OPI) No. 289367/1987 (the term "OPI" as used herein means an "unexamined published application"). In the technique, in order to prevent the difficulty that, in machining a high reflecting material with a laser beam, the laser beam is returned to the laser oscillator being partially reflected from the surface of the high reflecting material, thus increasing the stimulated emission of the laser beam, whereby the output produced becomes too high to be controlled, the angle of application of the laser beam to the workpiece is so controlled to be other than right angles. Therefore, the technique is similar to the present invention in that the laser beam is inclined with respect to the workpiece. However, the technique is fundamentally different from the present invention in the following points for instance:
(1) The object of the prior art disclosed by the Japanese Patent Application (OPI) No. 289367/1987 is different from that of the present invention. The material handled by the prior art is limited to the high reflecting material only.
(2) The prior art, having no machining program analyzing function, cannot adjust the posture of the machining head in cutting a curve, whereas the laser beam machine of the invention has a machining program analyzing function, thus being able to smoothly change the posture of the machining head in cutting such a curve.
(3) The laser beam machine of the present invention can change the angle of inclination of the laser beam according to the material and thickness of the workpiece and the machining speed, whereas the prior art has no such function.
With the laser beam machine of the invention, the laser beam is inclined at a predetermined angle in the machining direction at all times. As a result, the degree of curve of drag lines is reduced, and the quantity of dross stuck to the workpiece is deceased, whereby the machining speed can be increased as much. Furthermore for the same reason, the machining configuration is not limited, with the result that the machining productivity is greatly improved. In addition, in the laser beam machine of the invention, the angle of inclination of the laser beam can be determined best according to the material and thickness of the workpiece and the machining speed. Therefore, with the laser beam machine, even an operator not skilled in the laser beam machining operation can machine workpieces with high accuracy, and relatively thick workpieces can be machined with ease.
The nature, principle and utility of the invention will become more apparent from the following detailed description and the appended claims when read in conjunction with the accompanying drawings, in which like reference numerals or characters designate like parts.